Systems for optically sensing and decoding data have been known for some time. Portable systems are also known for optically sensing and decoding data. See U.S. Pat. No. 3,509,353 entitled Portable Record Reader by Sundblad et al., U.S. Pat. No. 3,716,699 entitled Method and Apparatus for Optical Code Reading by Eckert, Jr. et al., U.S. Pat. No. 3,736,410 entitled Hand Held Apparatus for Sensing Data Bits Carried on a Sheet by Ragland et al., U.S. Pat. No. 3,748,483 entitled Indicating Device for Use In Optical Sensing Equipment by Englund et al., U.S. Pat. No. 3,925,639 entitled Method and Apparatus for Reading Bar Coded Data Wherein a Light Source is Periodically Energized by Hester, U.S. Pat. No. 4,072,859 entitled Wand Turn-On Control by McWaters, and U.S. Pat. No. 4,160,156 entitled Method and Apparatus for Reading Bar Coded Data Wherein The Light Source Is Periodically Energized by Sherer.
These portable units have been used for data collection in a broad range of operations, from inventory control in retail stores to the more recent use in the tracking of packages or cargo for shipment purposes. These portable optical reading units typically are battery powered or attached to a terminal unit which supplies a power source.
To increase the accuracy of such data collection systems, codes have been produced and printed on products or containers. One such code is a "bar code" which may be read by passing an optical sensing unit over the bar code on the product or by passing the product over the optical sensing unit. These bar codes are patterned in a unique way in order to specifically identify the product or container.
A bar code typically consists of a pattern of dark and light bars of varying widths with the encoded information determined by the sequence of these varying width bars. These bars are scanned by the optical sensing unit and the widths of the bars are then translated into a specific identifying sequence for that particular product.
Notwithstanding many improvements, two problems have limited the use of portable bar code units. The first problem is that a portable unit must be battery powered. The optical sensing unit typically requires a source of radiation to illuminate the bar coded data which typically places a significant drain on the battery. As the applications of these portable optical sensing units continue to expand, users of such units continue to demand lighter weight, lower cost, and extended usage time from these units. Hence, the amount of power used by the radiation source and the accompanying sensing and decoding circuits continues to be a major obstacle in expanding applications.
A second problem is that because the bar code itself is a pattern of dark and light bars, optically reading these bars is often difficult in high ambient conditions, such as direct sunlight. The high ambient light interferes with the radiation source used to illuminate the bar coded data. When the optical sensing unit is passed across the code, the ambient light causes signal recognition errors or problems for the sensing unit and the data is not correctly decoded.
Therefore, there is a continued need for a low powered optical sensing unit that also greatly reduces the reading errors in these high ambient conditions.